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An object starting from rest travels $20\, m$ in first $2\,\sec $ and $160\, m$ in next $4\,\sec $. What will be the velocity after $7\,\sec $ from the start ?
$0.07 \,ms ^{-1}$
$700 \,ms ^{-1}$
$0.7 \,ms ^{-1}$
$70 \,ms ^{-1}$
Solution
$s_{1}=u t+\frac{1}{2} a t^{2}$ or $20=0+\frac{1}{2} a(2)^{2}$ or $a=10 \,ms ^{-1}$
$v=u+a t=0+(10 \times 2)=20\, ms ^{-1}$
$s_{2}=160=u t^{\prime}+\frac{1}{2} a^{\prime}\left(t^{\prime}\right)^{2}=(20 \times 4)+\left(\frac{1}{2} a^{\prime} \times 16\right) \Rightarrow a^{\prime}=10 \,ms ^{-2}$
since acceleration is the same, we have $v'=0+(10 \times 7)=70 \,ms ^{-1}$
Similar Questions
A truck is moving on a straight road with uniform acceleration. The following table gives the speed of the truck at various instants of time.
| Speed $\left(m s^{-1}\right)$ | $5$ | $10$ | $15$ | $20$ | $25$ | $30$ |
| Time $(s)$ | $0$ | $10$ | $20$ | $30$ | $40$ | $50$ |
Draw the speed-time graph by choosing a convenient scale. Determine from it
$(i)$ the acceleration of truck
$(ii)$ the distance travelled by the truck in $50$ seconds.
